You'll need to connect to the server via the console.
To do this, enable the developer console in the options menu.
Then, bring the console down with the ` key.
type "connect SERVER IP HERE"
It'll connect you and use your slot, kicking a non slot person.
Enjoy.

[13:58] TheSpaniard84: I have a kitty stuck to my rump
[13:58] WhuTdufK: I suppose that's better than what's normally stuck to your rump.